The role of intergenerational influences on age at menarche has not been explored far beyond the association between mothers'and daughters'menarcheal ages. Small size at birth and childhood obesity have been associated with younger age at menarche, but the influence of maternal overweight or obesity on daughters'age at menarche has not been thoroughly examined. We followed girls who were born as subjects in the Philadelphia and Providence centers of the Collaborative Perinatal Project (daughters were born 1959-66) in 1987. As part of the follow up they were asked their age at menarche Compared with those whose mothers had a BMI less than 25, daughters of obese mothers experienced younger age at menarche (OR for menarche at <or=12 years = 3.1 1.1-9.2). This association remained after adjusting for maternal age at menarche, maternal parity, socioeconomic status, race, and study site (OR = 3.3 1.1-10.0). Effect estimates for maternal overweight were close to the null. There was limited evidence of mediation by small for gestational age or BMI at age 7. This suggests that maternal obesity is associated with younger menarcheal age among daughters in this study, possibly via unmeasured shared factors. We also found that girls whose mothers smoked experienced later age at menarche, in contrast to previous research which found the opposite.